Thyroid and Antithyroid Drugs

Question 1

5’ deiodinase enzymes are inhibited by?

Answer 1

1. Drugs such as propylthiouracil, propanolol, corticosteroids, and amiodarone
2. Severe illness and starvation
3. Iodinated compounds such as radiographic agents iopanioc, iopanoic acid, and ipodate

Question 2

How is hypothyroidism managed and what are the preperations classified into?

Answer 2

• Tx by thyroid hormone replacement

1. Synthetic preparations
   
   1. Levothyroxine (T4) DOC
   2. Liothyronine (T3)
   3. Liotrix (mixture of T4 and T3
2. Natural prepartation of animal origin

Question 3

What are the adverse effects of thyroid replacement therapy?

Answer 3

• hyperthyroidism like manifestation
• Increased risk of atrial fibrillation and osteoporosis

Question 4

Why is a higher dose of levothyroxine usually required during pregnancy?

Answer 4

1. Increased serum concentration of Thyroxine-binding globulin (TBG) induced by estrogen
2. Expression of 5’ deiodinase 3 (D3) by the placenta
3. Small amount of transplacental passage of levothyroxine from mother to fetus

Question 5

What are the primary methods of controlling hyperthyroidism?

Answer 5

1. Pharmacotherapy
2. Destruction of the gland with radioactive iodine (RAI)
3. Surgical thyroidectomy

Question 6

What are the types of drugs used to manage hyperthyrodism?

Answer 6

• Thioamides
• Iodides
• Beta-adrenoreceptor blocking agents
• Glucocorticoids
• Bile acid sequestrants

Question 7

Thioamides MOA, Uses, AE

Answer 7

• Methimazole - DOC unless first trimester pregenacy or thyroid storm
• Propylthiouracil (PTU) - also inhibits peripheral diodination so preferred for severe hyperthyroidsim and thyroid storm

MOA: inhibitor of thyroid peroxidase enzyme

Uses: Tx of hyperthyroidism, conjunction with radioacitve iodine, and to control hyperthyroidism in preperation of surgical treatment

AE: urticarial rash, agranulocytosis, hepatotoxicity, vasculitis, tetragenicity

Question 8

Iodides MOA, Uses, AE

Answer 8

MOA: inhibit hormone release from thyroid gland and should not be used alone because thyroid gland escapes block in 2-8wks

Uses: thyroid storm, preoperative preparation for surgery, radiation emergencies involving relase of radioactive iodine isotopes

AE: uncommon, hyperthyroidism, hypothyroidism, delay onset of thiomide therapy, fetal goiter is used during pregnancy

Question 9

Beta-Adrenoceptor blocking agents uses

Answer 9

• Propranolol - inhibits the conversion of T4 to T3
• Diltiazem/Verapamil - control tachycardia

Uses: extensible alleviate catecholamine excess-like manifestations

Question 10

Glucocorticoids MOA, Uses

Answer 10

MOA: inhibit the peripheral conversion of T4 to T3 and promote vasomotor stability

Uses: management of Grave’s opthalmopathy and dermopathy

Question 11

Bile Acid Sequestrants MOA, Uses

Answer 11

• Cholestryamine

MOA: bind to and prevent the enterohepatic cycling of thyroid hormones

Uses: management of thyroid storm

Question 12

Radioactive Iodine MOA, Uses, AE

Answer 12

MOA: destroys thyroid parenchyma

Uses: preferred treatment of hyperthyroidism

AE: hypothyroidism, radiation thyroiditis, exacerbate Grave’s opthalmopathy, destroy the fetal thyroid during pregnancy

Question 13

What is a thyroid storm and was triggers it?

Answer 13

• Sudden life-threatening acute exacerbation hyperthyroidism
• in pts with hyperthyroidism triggered by infection, trauma, surgery, physical illness, and severe emotional distress